From U.S. Pat. No. 4,246,221 the dry wet spinning of solutions of cellulose in N-methylmorpholine-N-oxide/water mixtures is known. With this process the stretch ratio in the non-precipitating medium between the spinneret and the coagulation bath is to be at least 3 (col. 3, lines 46-47 47). The numerical values for the stretch ratio given in the examples are in the range from 2.6 to 798. The thickness of the layer of the non-precipitating medium between the spinneret and the coagulation bath is quoted 50 and 305 mm, respectively, and the diameters of the spinneret holes are 250 .mu.m and 305 .mu.m, respectively, and the diameters of the spinneret holes are 250 .mu.m and 1000 .mu.m, respectively. From Table VI can be gathered that spinning with a low spin-stretch ratio does not yield satisfactory fiber properties. With a stretch ratio of 2.6 the wet modulus at 5% is only 3.1 whereas a value of at least about 7 would be satisfactory. This, U.S. Pat. No. 4,246,221 teaches to use high spin-stretch ratios to achieve good fiber properties.
U.S. Pat. No. 5,252,284 teaches to improve the fiber or filament characteristics with the process mentioned here-above by extruding a solution of cellulose through a nozzle orifice having a length of at least 1000 .mu.m and a minimum diameter along said length of at most 150 .mu.m. A cylindrical section having this minimum diameter is formed at the outlet end of said nozzle orifice and has a minimum length of 1/4.times.1000 .mu.m=250 .mu.m. In example 6 this length is 430 .mu.m with its diameter being 50 .mu.m. According to col 3, lines 1 to 4, the orifice passage must be so elongated and of such small diameter that the generated shear forces acting on the solution flowing through the passage result in a significant preorientation of the cellulosic polymer. As the spinning pressure of the solution to be maintained upstream of the nozzle is proportional to the length of the passage section having said small diameter, the process requires high spinning pressures in the order of 100 to 1200 bar. These high spinning pressures are a considerable drawback for a spinning process on a commercial scale.
It is known that the surface structure of a fiber is to a high degree responsible for the textile properties of the products fabricated from the fiber. E.g. the gloss and the feel of a textile article are strongly affected by the morphologic structure of the fiber surface. Viscose rayon has a multiple lobate surface structure, the constrictions at the fiber surface extending in the longitudinal direction of the fiber. This surface structure of the viscose fiber results in satisfactory textile properties such as e.g. sufficient fiber adhesion with their spinning to fiber yarns, a satisfactory thread connection with filament yarns and a sufficient non-slip property of flat-shaped articles made from these yarns.
Jacquinet in U.S. Pat. No. 3,579,625 discloses a process for forming trilobal filaments consisting of cellulose esters. This pure dry spinning is a completely other process than the dry wet spinning and affects the filament profiling in a different manner. The aim of such profiling is to impart high resilience to these filaments.